This invention relates to vapor compression cycle devices and more particularly to a means and a method for controlling the modulation of both thermal capacity and evaporator superheat in such a device.
In a conventional vapor compression cycle device such as a heat pump a working fluid liquid is circulated through an expansion device into an evaporating heat exchanger where the working fluid absorbs heat. The heat vaporizes the working fluid liquid, and the resulting vapor is then circulated by a suitable compressor through a condensing heat exchanger where the vapor condenses into a liquid as heat is given off. The cycle is then repeated as the working fluid is recirculated through the system.
The quantity of heat required to vaporize the working fluid liquid is known as the heat of vaporization. Additional heat absorption by the resulting working fluid vapor causes an increase in the vapor temperature above the temperature of vaporization. This increase in vapor temperature is defined as superheat.
In conventional vapor compression cycle devices it is desirable to control the amount of superheat in the device cycle to achieve optimum system performance. Typically this control of superheat is effected by regulating the flow rate of working fluid liquid passing through the expansion device to the evaporator.
A vapor compression cycle device should also include means to modulate the capacity of the device to absorb and deliver heat, herein referred to as device thermal capacity, in response to variable heating and cooling demands in order to maximize efficiency. A device of this type is disclosed in U.S. Pat. No. 4,217,760. The thermal capacity of this device is modulated by regulating the amount of a multi-component working fluid allowed to flow from a first accumulator through an evaporator to a second accumulator located at a compressor inlet. As described in the cited application, this results in a change in the molar flow rate through the compressor and thus a change in device thermal capacity.
A device which includes means both for modulating device thermal capacity and for controlling the amount of evaporator superheat generated therein is disclosed in a later filed co-pending application Ser. No. 052,971, filed June 28, 1979, which is also assigned to the same assignee as the present invention. As in the earlier disclosed device described above, this latter device includes two accumulators. However, the second accumulator in the latter device is relocated intermediate two stages of an evaporating heat exchanger, and is adapted to decrease the time required to switch the device from a high to a low capacity mode of operation. Additionally, the evaporator superheat of the latter device is controllable through regulation of the amount of working fluid liquid allowed to flow from the second accumulator into the final evaporator stage.
The device disclosed in co-pending application Ser. No. 52,971 thus includes means whereby both evaporator superheat and device thermal capacity can be variably controlled. However, optimal performance of this device can require the coordinated adjustment of a plurality of flow restricting devices in response to sensed conditions.
Accordingly, it is an object of this invention to provide a new and improved means for controlling the modulation of the thermal capacity of a vapor compression cycle device.
Another object of the present invention is to provide a new and improved means for controlling the evaporator superheat of such a device.
Still another object of the present invention is to provide a new and improved means and method for the control of a vapor compression cycle device thermal capacity and evaporator superheat.